What do I mean? Most churches offer a safe, nurturing community, an oasis of stability and predictability. Studies show that women and seniors are the groups most likely to seek these things. Our comforting congregations provide women with what they long for, so naturally they show up in large numbers.
On the other hand, men and young adults are drawn to risk, challenge, and daring. While our official mission is one of adventure, the actual mission of most congregations is making people feel comfortable and safe – especially longtime members (Pastors, can I have an amen?) Church insiders routinely block anything challenging or innovative because it might make people feel uncomfortable or unsafe. This caution keeps the peace in the short term, but it drives men and young adults away over the long term.
Then there's our reputation as a place for little old ladies of both sexes. Many guys feel church is a "women's thing." Most men are introduced to Christianity by women – nuns, nursery workers, Sunday school teachers, and mom. Boys meet a feminized Jesus – a tender, sweet man in a shining white dress. Most volunteer opportunities in church involve traditionally female roles: singing, sewing, cooking, caring for children, teaching, planning social gatherings, etc. There's nothing for a guy to do – unless he has a passion for attending meetings or passing out bulletins.
The "gender gap" is pretty visible in the US Catholic Church, and in Western Europe, I'd say (Especially when it comes to mid-level church workers!) Not so, at least in my brief experience, here in India, based on Mass attendance. Something to do with secularization? As the cultural pressure for church attendance decreases, males stop being involved? I dunno. t does seem to be more of a problem in the West than in parts of the Global South, at least as far as Asia and Africa go. In the experience of my (Hindu) family, as far as ritual participation goes, the women do everything, while the men look on. Not that Hinduism is a "women's religion" (in as much as one can call it a religion). And certainly not Islam. And besides, gender-role distinctions are pretty strong in Indian society. Sorry, couldn't resist the superficial insta-analysis. :)
Anyway, I don't know exactly how to define the problem, don't know enough about the history of such trends, or how to change things. In Catholic circles sometimes the discussion tends to focus on "manly priests" as opposed to those who seem enamored by too much lace. One thing on the site made me smile: the suggestion that sermons be short. At least in my experience, Catholic homilies are rarely much longer! And, at least as far as I can tell, in many African-American congregation, the sermons are much longer. Is that a deterrent to black men participating in church? I don't know.
Most what I've read makes me want to go, like a fake pirate, "Arrr! We need to be more masculine!" and flex my (non-existent) muscles, belch loudly and reach for the nearest can of Bud.